There are abundant of water-related energy sources in the environment including, for example, ocean wave, tide, waterfall, and rainwater. Each water source may carry multiple types of energy. For example, a single water drop carries two types of energy, including mechanical kinetic energy and electrostatic energy owing to triboelectric charges caused by its contact with surrounding media.
Since 1867, the Kelvin water dropper has been invented to collect the water electrostatic energy and illustrate the natural generation of electricity in atmospheric phenomena such as thunderstorms. The Kelvin water dropper uses falling water to generate a potential difference by electrostatic induction between two interconnected, oppositely charged systems, and it utilizes the initial instantaneous non-equilibrium status of charge distributions in the liquid rather than the friction between the liquid and air.
Recently, triboelectric nanogenerator (TENG) has been developed to convert mechanical vibration energy into electricity. The working mechanism of TENG is based on a combination of contact electrification and electrostatic induction. Normally, TENG needs a relatively dry condition to provide a stable output, because the surface triboelectrification would be largely reduced or totally eliminated owing to the presence of water.
There is a need for a new prototype TENG to harvest water-related energy. There is also a need to maximize the TENG's output by converting both mechanical kinetic energy and electrostatic energy from water into electricity.